Production of collagen strands



PRODUCTION OF COLLAGEN STRANDS Application January 19, 1955, Serial No.482,881

11 Claims. (Cl. 18-47.5)

No Drawing.

This invention relates to new and useful improvements in the productionof collagen strands, and is a continuation in part of our co-pendingapplication, Serial No. 152,014, filed March 25, 1950, now abandoned.

It has been proposed to produce strands from collagenous material suchas tendons. These strands, however, did not have the strength of qualityrequired for many purposes. In accordance with one proposed process, thetendons or pieces thereof were directly subjected to the action of anacid to loosen the coherence of the individual fibers of the bundles andthereafter pressed out into bands. The acidulation in this manner,however, seriously weakened the fiber structure and thus the strength ofthe end product produced.

One object of this invention is the production of collagen strands whichare characterized by their enormous strength and ability to withstandstresses and which may be used as the substitute for high-grade catgut.This, and still further objects, will become apparent from the followingdescription.

The term strands is used herein to generically designate any elongatedmembers such as filaments, strings, threads, etc.

The starting collagenous material for the formation of the strands inaccordance with the invention comprises animal tendons, such as cattleor horse tendons.

In accordance with the invention the starting animal tendons aredisintegrated into fibers, preferably while adding sufficient coolingwater to prevent heating and to thereby produce a very thin fibersuspension. This fiber suspension, after the separation of any surpluswater, is acidulated by mixing with acid to a pH of between 2.5 and 4.5to form a swollen mass. The swollen mass is then diluted with water toform a castable mass which is cast into a thin foil. The foil is thenformed into a strand as, for example, a filament or thread by splittingthe same into narrow strips and twisting the strips.

The starting tendons are preferably freed from the flesh residues and,if necessary, from the sheaths and are cut into small pieces. Thesepieces are then disintegrated into the fibers as, for example, with theuse of mills or other suitable arrangement as, for example, toothed-discmills, wing beater mills, hammer mills, pan grinders, edge mills, orrolling mills with rifled rolls. If the tendons are salted, they shouldbe first washed free from the salt prior to the disintegration.

The disintegration proper as, for example, in the mill must be eifectedso that substantial heating of the material does not occur. Thedisintegration is preferably effected with simultaneous cooling as, forexample, by feeding a sufiicient amount of cooling water into themill'to avoid heating of the fibrous mass produced and to form a thinfiber suspension.

The initial disintegration must be effected by a purely mechanicalprocess and chemicals such as acids should not be used.

The fibrous material from the disintegration as, for example, the thinfibrous suspension from which the nited States Patent "ice surplus waterhas been removed as, for example, with the use of a strainer, centrifugeor filter press is subjected to acidulation.

The acidulation may, for example, be effected with hydrochloric acidand, if necessary, with the addition of water while the fiber pump isbeing worked up as, for example, in a kneader-mixer or vessel providedwith an agitating mechanism or the like.

The acidulation must be effected at a pH between 2.5 and 4.5, andpreferably at a pH of about 3.5.

By effecting the disintegration of the tendons into fibers mechanically,as described above and without the use of chemicals such as acids, andby only eflfecting the acidulation after this disintegration using a pHbetween 2.5 and 4.5, the fibrous material is converted into a uniformlyswelled mass which has the appearance of a homogenous turbid ortranslucent mass, the viscosity of which may range according to drycontent from that of a thin machine oil to that of a dough which is justcapable of flowing. The swollen mass may, for example, somewhat resemblea White gell or slime.

By effecting the acidulation in the manner described, the water presentin the fiber pulp is absorbed by the fibers, causing them to swell andforming a uniformly swollen mass from which the swelling water can nolonger be mechanically removed as, for example, by being filtered off orpressed otf.

If the swollen mass formed by acidulation has not been made sufiicientlyhomogenous by the working up in the beater or mixer, it may be furtherworked and homogenized by treatment as, for example, on a pair ofrollers or by pressing through nozzles or perforated plates.

The swollen mass is then diluted with Water to form a castable masswhich should have a dry matter content of between 0.5 and 2%, andpreferably between 0.5 and 1%. The addition of this water to form acastable mass is preferably effected with simultaneous intimate mixingas, for example, in an agitating mechanism. The castable mass thusformed appears homogenous and the individual fibers cannot be observed.The mass, for example, appears as a white, translucent liquid having anoil-line consistency.

If desired, materials which influence the characteristics of the strandsas, for example, disinfectants, plasticizers, oil or fat emulsions,tanning agents, etc. may be introduced into the castable mass. Theintroduction may be effected simultaneously with the introduction of thediluting water as, for example, by evenly distributing the material inthe water. Conversely, the material may be added to the castable massafter the same is formed or separately at the same time the water isadded.

The castable mass should be freed from any air present as, for example,by allowing the same to stand, by centrifuging or the like. In the caseof castable masses having a higher solid content as, for example, 1-2%,the removal of the air is somewhat more difiicult and high speedcentrifuging may be required.

The casting of the mass into the thin foil may be effected in anyconventional manner as, for example, by spreading the mass in the formof a thin film on a support as, for example, a casting band and dryingit. The casting is, however, preferably effected in a conventional filmcasting machine as, for example, by introducing the mass into thecasting frame.

The drying of the film may be effected in any conventional manner as,for example, by blowing heated air over the mass, passing the castingband through drying channels or the like. The thickness of the film orfoil to be produced may be adjusted by adjusting the dry content of thecastable mass, adjusting the casting slot, etc. Thicker films may beproduced by spreading the castable mass .in two or more layers on thedried films. The films of, for example, the thickness of about have beenfound preferable in the further working up into catgut and similarproducts.

After the casting, the foil produced may, for example, resemble a pieceof cellophane if the casting is effected on a smooth support such as aglass surface. When the casting is effected on a casting machine, thethin foil ribbon has a somewhat textured appearance.

The foil may be wound up on spools for storage or may be immediatelyfurther worked up.

-For the purpose of producing strands such as catgut, strings formusical instruments, tennis racquets, textile filaments for specialpurposes and the like, the foil coming from the casting band in thedried condition or un- Wound from astorage spool may, for example, becut into narrow strips, for example 1-30 in width in a longitudinaldirection. The cutting may be effected, for example, with a conventionalfilm cutting machine. The width of the narrow strips depends on thedesired thickness of the end strands to be produced. Narrow strips will,of course, form thinner strands and wider strips, thicker strands.Strands are then produced from the narrow strips in a known manner bytwisting, i. e. spinning the strips, which have preferably beenmoistened.

The moistening of the strips may be effected with pure water or withwater to which suitable additives have been incorporated as, forexample, alcohols for inhibiting swelling, basically active substancescounteracting the acid swelling, disinfectants such as iodine or iodinecompounds, reducing agents, tanning agents and the like. These additivesmay be employed separately or in any desired combination.

The spinning may also be effected by twisting a number of stripstogether to form a single strand. It is thus possible to producefilaments of different thicknesses from narrow strips.

In order to produce strands of great strength, it is preferable to carryout the drying with increasing tension. The elemental fibers are thusdirected more or less substantially parallel to the axis of thefilament, i. e. linearly aligned, which produces a considerable increasein the breaking strength.

Upon drying, strands of great strength are obtained which maybeemployed, for example, as a substitute for catgut, as strings formusical instruments, tennis racquets and the like, or for specialpurposes in the textile industry.

The strands as, for example, filaments resemble high quality catgut andhave a tearing strength in excess of 50 kilograms per square millimeter.

A particular important field of application for use of the strandsproduced in accordance with the invention is as surgical sutures whichare reabsorbed in the human or animal body in exactly the same way ascutgut produced from sheep intestines. The rate of reabsorption can beadjusted by varying the degree of tanning. Untanned strands arereabsorbed much more quickly than catgut produced from sheep intestines.Such strands are consequently suitable for ligatures in tissues in whichit is desirable that they disintegrate and be reabsorbed within a shorttime as, for example, within a few hours. As has already been stated,tanning or hardening may most suitably take place in accordance with theinvention by adding tanning agents during the manufacturing-process,particularly atthe time of the formation of the castable mass. Thefinished, untanned strands may also be subsequcntly tanned with anyknown tanning agent, in which connection there arepreferably employedtanning agents which do not have an immediate tanning agent but whichcan later be givena tanning action, as, for example, by a .pH adjustmentor by reduction as, for example, in the case of chromates such as sodiumdichromate. The surgical strands produced in accordance with theinvention are not subject to the sterilization ditficulties of theconventional sheep intestine catgut.

The process in accordance with the invention is extremely simple andreliable and no disturbing decomposition of the collagen takes place.

The following examples are given by way of illustration and notlimitation:

Example 1 Cattle and horse tendons were washed free from salt, freedfrom the flesh residues and sheaths and cut into small pieces. Thesepieces were disintegrated in a mill while adding sufficient coolingwater to prevent heating. A thin suspension of the tendon fibers wasrecovered from the mill. This fiber suspension was freed from excesswater with the use of a filter press, forming a fiber pulp. The fiberpulp was placed in a vessel provided with a mixer and hydrochloric acidand water were added to form a pH of about 3.5. After the addition ofthe acid the fibers commenced to swell, forming a uniformly swollen masswhich had the appearance of a white gell or slime.

The swollen mass was intimately mixed with water in a vessel providedwith an agitating mechanism. An amount of water was added to form a drycontent of about O.5l%. Upon this dilution a castable mass whichappeared as a homogeneous, white, translucent liquid having an oil-likeconsistency appeared. The individual fibers could not be observed inthis castable mass.

The mass was fed into the casting frame of a conventional film castingmachine and, after drying, a foil having a thickness of about 10p. wasformed. The dry foil was cut into strips of about 15 mm. width. Thestrips were moistened with water and spun by twisting into a strandwhich had the appearance and characteristics of a'high quality catgut.

Example 2 A'swollen mass was produced in the manner described in Example1 by the disintegration and acidulation of the animal tendons. Theswollen mass was diluted in a mixerwith water to a dry content of about1.5%. The diluting water additionally contained polyethylene glycolamounting to 5% calculated on the dry collagen and having a molecularWeight of 2,000. The castable mass thus formed was freed from air andcast on the band of a film casting machine. After drying, a foil of 25p.thickness was formed. The foil was cut into bands of 25 mm. thicknessand five such bands were moistened and spun together by twisting into athread. The added polyethylene glycol had an excellent softening effecton the strand which constituted a higher quality string suitable for theproduction of tennis racquets.

Example 3 A swollen'mass was formed by disintegration and acidulation oftendons in the manner described in Example 1. The mass was diluted withwater'in a mixer to a dry content of 2%. The mass had a high viscosityand was freed from the entrapped air by cetrifuging at high speed. Themass was applied evenly under high pressure from a flat nozzle to theband of a fiat casting machine. After drying, a foil was produced havinga thickness of 40 The foil was cut into longitudinal strips havingwidths of 30 mm. and eight such strips were passed through a bathcontaining 10 parts of glycerin and parts of water. The wetted stripswere then spun by twisting into a thread and dried. The end thread had athickness of 3 mm. and was polished on a polishing machine to a uniformthickness of 2.8 mm. The string produced constituted a higher qualitystrength suitable, for example, as a cello string.

The above description has been given in order to illustrate and notlimit the invention, and various embodiments and modifications willbecome apparent to the skilled artisan which fall within the spirit ofthe invention and the scope of the appended claims.

We claim:

1. Process for the production of collagen strands from animal tendonswhich comprises mechanically disintegrating tendons into fibers,acidulating the fibers within a pH range of about 2.5-4.5 by mixing thefibers with acid to form a swollen mass, diluting said swollen mass withwater to form a castable mass, casting said mass into a thin foil, andforming strands from said foil.

2. Process according to claim 1, in which said disintegration iseffected while adding sufficient cooling water to prevent heating andthereby produce a thin fiber suspension, and in which the surplus wateris separated from said fiber suspension prior to said acidulation.

3. Process according to claim 1, in which said swollen mass .is dilutedwith water to form a castable mass having a dry matter content of 0.52%

4. Process according to claim 1, in which said strands are formed bysplitting siad foil into narrow strips, moistening the strips andforming filaments from said strips by twisting.

5. Process according to claim 1, in which said acidulation is effectedto a pH of about 3.5.

6. Process according to claim 1, in which said swollen mass is dilutedwith water to form a castable mass having a dry matter content of 0.51%

7. Process according to claim 1, in which a tanning salt of chromium isincorporated into the strand.

8. Process according to claim 1, in which a tanning agent isincorporated in latent form into the strands during the formationthereof and is later rendered active in the completed strands.

9. A process for the production of filaments and strings from animaltendons which comprises disintegrating tendons into fibers while addingsufiicient cooling water to prevent heating and thereby produce a verythin fiber suspension, separating and removing the surplus water fromsaid fiber suspension, mixing the fibers with acid to a pH range of2.5-4.5 to form a swollen mass, diluting said swollen mass with water toform a castable mass having a dry matter content of 0.5-1%, casting saidmass into a thin foil, slitting said foil into narrow strips, andforming filaments from said strips by twisting the strips.

10. Process according to claim 9, in which a tanning salt of chromium isincorporated in the material.

11. Process according to claim 9, in which a tanning agent isincorporated in latent form into the filaments during the formationthereof, and is later rendered active in the completed filaments.

No references cited.

1. PROCESS FOR THE PRODUCTION OF COLLAGEN STRANDS FROM ANIMAL TENDONSWHICH COMPRISES MECHANICALLY DISINTEGRATING TENDONS INTO FIBERS,ACIDULATING THE FIBERS WITHIN A PH RANGE OF ABOUT 2.5-4.5 BY MIXING THEFIBERS WITH ACID TO FORM A SWOLLEN MASS, DILUTING SAID SWOLLEN MASS WITHWATER TO FORM A CASTABLE MASS, CASTING SAID MASS INTO A THIN FOIL, ANDFORMING STRANDS FROM SAID FOIL.